1. Field of the Invention
The present invention relates to a sole of a baseball spiked shoe, and a method of measuring shearing stress distribution of a baseball spiked shoe. More particularly, the present invention relates to the sole of baseball spiked shoes that provides superior sliding resistance in any action in a baseball play such as batting, throwing, and running, and that improves flexibility of the foot action during the play. Also, the present invention relates to a method of measuring shearing stress distribution of a baseball spiked shoe.
2. Description of the Background Art
Conventional baseball spiked shoes, particularly those with metal spikes, have the so-called triangular shaped blades provided on the sole. More specifically, as shown in FIG. 17A, three blade-like protrusions at respective positions at the fore foot portion and the heel portion are joined by a connecting washer so as to be located at the vertices of a triangle, and fastened by a fixing pin and the like at respective holes formed in the connecting washer.
A baseball spiked shoe as shown in FIG. 17B is also used. Such a baseball spiked shoe has the triangular shaped blades of the fore foot portion divided into a toe portion spike and a stepping portion spike in order to improve the flexibility of the fore foot portion of the shoe sole.
Also, a baseball spike shoe having auxiliary projections provided to the conventional triangular shaped blades as shown in FIG. 18 for the purpose of improving sliding resistance is disclosed in Japanese Patent Laying-Open No. 6-21408.
A baseball shoe with the above-described triangular shaped blades had almost no flexibility at the fore foot portion since a connecting washer of high rigidity is fixed over a large area at the fore foot portion from the toe portion to the stepping portion. When a person wearing such baseball spiked shoes shifts his or her weight frontward at the time of running to kick the ground, his or her foot will move within the shoe since the sole cannot accurately follow the flexing fore foot portion. The initial kicking force cannot be reliably conveyed against the ground.
A similar problem is encountered when the player moves sideways. The shoe sole cannot accurately follow the eversion and inversion shape of the foot portion. The foot will move inside the shoe, so that the kicking force cannot be reliably conveyed against the ground. Such disadvantages could not be solved by the baseball spiked hardware disclosed in the aforementioned Japanese Patent Laying-Open No. 60-21408.
The typical actions during a baseball play are the four actions of batting, throwing, fielding, and running. The strength of a player's leg could not be exercised sufficiently in respective actions with the conventional worn spiked shoes. For example, when a right-handed batter is at bat, the right foot functions as a pivoting foot to exhibit a great kicking force centering about the anterior portion of the first metatarsal head at the time of ball-impact. However, since there is no projection in a conventional spiked shoe at the anterior portion of the first metatarsal head and the projection provided in the proximity of the first metatarsal head is provided parallel to the direction of the kicking force, a great force cannot be generated. The shoe sole will slide on the ground to result in loss of the kicking force.
When a right-handed player throws a ball, a great kicking force is imparted from the stepping portion to the heel portion of the right foot in the action starting from take back to the down swing of the player's arm. At the moment the ball leaves the player's hand, a great braking force is imparted from the heel portion to the stepping portion of the left foot. Since a conventional spiked shoe has only one projection provided at the toe portion, which is located at right angles with respect to the longitudinal line of the foot, the kicking force at the toe portion of the right foot could not be conveyed sufficiently against the ground. Furthermore, there is only one projection provided as perpendicular to the longitudinal line of the foot at the heel portion of the left foot shoe, so that a sufficient braking force could not be exercised.
As to the kinetic performance of a baseball player during fielding and running, the movement can be classified into the case where the player makes a dash straight forward, and the case where the player turns his body and makes a dash in that direction. When the player dashes straight forward, the load path on the sole of the spiked shoe shows a trajectory starting from contact of the heel on the ground to the toe portion via the lateral side of the plantar arc, the lateral side of the stepping portion, and the medial side of the stepping portion.
Although a conventional spiked shoe has a projection provided at the first metatarsal head, the direction of the projection is parallel to the direction of the transfer of weight. An adequate kicking force could not be exercised, resulting in loss of force. When the player makes a dash sideways in the right direction, the region of the left foot from the toe portion to the medial side of the stepping portion kicks against the ground while the toe of the right foot is pointed towards the forwarding direction to dart off. Since the projections provided at the first metatarsal head and at the toe of a conventional spiked shoe are substantially parallel to the direction of the kicking force, there was loss in force.
Although flexibility corresponding to various movements is required in spiked shoes, the sole of a conventional spiked shoe does not have a flexion groove provided at an effective position.